Tidally induced warps of spiral galaxies in IllustrisTNG

Abstract Warps are common features in both stellar and gaseous discs of nearby spiral galaxies with the latter usually easier to detect. Several theories have been proposed in the literature to explain their formation and prevalence, including tidal interactions with external galaxies. Observational correlations also suggest the importance of tides for warp formation. Here, we use the TNG100 run from the magnetohydrodynamical cosmological simulation suite IllustrisTNG to investigate the connection between interactions and the formation of gas warps. We find that in the sample of well-resolved gas-rich spiral galaxies (1010 ≲ M*/M⊙ ≲ 1011 at z = 0) from the simulation TNG100-1, about 16% possess the characteristic S-shaped warp. Around one-third of these objects have their warps induced by interactions with other galaxies. Half of these interactions end with the perturber absorbed by the host by z = 0. We find that warps induced by interactions survive on average for <1 Gyr, similarly to the remaining S-shaped warps. The angle between the orbital angular momentum of the perturber and the angular momentum of the host’s disc that most likely leads to warp formation is around 45 degrees. While our main goal is to investigate tidally induced warps, we find that during interactions in addition to tides, new gas that is accreted from infalling satellites also can contribute to warp formation

Always on the tipping point : A search for signals of past societies and related peatland ecosystem critical transitions during the last 6500 years in Poland

The research was funded by a grant from the National Science Centre (Poland) (No 2015/17/B/ST10/01656). The work was also made in the framework of the National Programme of Development of Humanities project (No 2bH15015483) as well as budgetary sources for scientific activity in 2016–2019, project number 0342/IP1/2016/74. V.E.J.J. was supported by the French National Research Agency (MIXOPEAT project, grant number ANR-17-CE01–0007). We thank Julie Loisel help with the calculation of the peat carbon accumulation rates. We thank also Jerzy Sikora and Paweł Zawilski for defining the chronology of the potsherd found during field surveys in the Głęboczek vicinity, and Sambor Czerwiński for constructing the lidar terrain map of the study area.Peer reviewedPublisher PD

Study of the Sextans dwarf spheroidal galaxy from the DART CaII triplet survey

We use VLT/FLAMES intermediate resolution (R~6500) spectra of individual red giant branch stars in the near-infrared CaII triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (+- 2 km/s) and CaT [Fe/H] measurements (+- 0.2 dex). We use the MgI line at 8806.8 \AA\, as an empirical discriminator for distinguishing between probable members of the dSph (giant stars) and probable Galactic contaminants (dwarf stars). Sextans shows a similar chemo-dynamical behaviour to other Milky Way dSphs, with its central regions being more metal rich than the outer parts and with the more metal-rich stars displaying colder kinematics than the more metal-poor stars. Hints of a velocity gradient are found along the projected major axis and along an axis at P.A.=191 deg, however a larger and more spatially extended sample may be necessary to pin down the amplitude and direction of this gradient. We detect a cold kinematic substructure at the centre of Sextans, consistent with being the remnant of a disrupted very metal poor stellar cluster. We derive the most extended line-of-sight velocity dispersion profile for Sextans, out to a projected radius of 1.6 deg. From Jeans modelling of the observed line-of-sight velocity dispersion profile we find that this is consistent with both a cored dark matter halo with large core radius and cuspy halo with low concentration. The mass within the last measured point is in the range 2-4 x 10^8 M_sun, giving very large mass-to-light ratios, from 460 to 920 (M/L)_(V,sun).Comment: 30 pages, 17 figures; 4 tables. Accepted for publication in MNRAS. Table 4 will appear as online material in the published version of the manuscript. Typo correcte

Discrepant Mass Estimates in the Cluster of Galaxies Abell 1689

We present a new mass estimate of a well-studied gravitational lensing cluster, Abell 1689, from deep Chandra observations with a total exposure of 200 ks. Within r=200 h-1 kpc, the X-ray mass estimate is systematically lower than that of lensing by 30-50%. At r>200 h-1 kpc, the mass density profiles from X-ray and weak lensing methods give consistent results. The most recent weak lensing work suggest a steeper profile than what is found from the X-ray analysis, while still in agreement with the mass at large radii. Previous studies have suggested that cooler small-scale structures can bias X-ray temperature measurements or that the northern part of the cluster is disturbed. We find these scenarios unlikely to resolve the central mass discrepancy since the former requires 70-90% of the space to be occupied by these cool structures and excluding the northern substructure does not significantly affect the total mass profiles. A more plausible explanation is a projection effect. We also find that the previously reported high hard-band to broad-band temperature ratio in A1689, and many other clusters observed with Chandra, may be resulting from the instrumental absorption that decreases 10-15% of the effective area at ~1.75 keV.Comment: 18 pages, 15 figures. ApJ accepte

The X-ray Cluster Normalization of the Matter Power Spectrum

The number density of galaxy clusters provides tight statistical constraints on the matter fluctuation power spectrum normalization, traditionally phrased in terms of sigma_8, the root mean square mass fluctuation in spheres with radius 8 h^-1 Mpc. We present constraints on sigma_8 and the total matter density Omega_m0 from local cluster counts as a function of X-ray temperature, taking care to incorporate and minimize systematic errors that plagued previous work with this method. In particular, we present new determinations of the cluster luminosity - temperature and mass - temperature relations, including their intrinsic scatter, and a determination of the Jenkins mass function parameters for the same mass definition as the mass - temperature calibration. Marginalizing over the 12 uninteresting parameters associated with this method, we find that the local cluster temperature function implies sigma_8 (Omega_m0/0.32)^alpha = 0.86+/-0.04 with alpha = 0.30 (0.41) for Omega_m0 < 0.32 (Omega_mo > 0.32) (68% confidence for two parameters). This result agrees with a wide range of recent independent determinations, and we find no evidence of any additional sources of systematic error for the X-ray cluster temperature function determination of the matter power spectrum normalization. The joint WMAP5 + cluster constraints are: Omega_m0 = 0.30+0.03/-0.02 and sigma_8 = 0.85+0.04/-0.02 (68% confidence for two parameters).Comment: 31 pages, 16 figures, accept for publication in ApJ 609, Jan. 10, 200

Diffuse light and building history of the galaxy cluster Abell 2667

We have searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three filters. We have applied to these images an iterative multi-scale wavelet analysis and reconstruction technique, which allows to subtract stars and galaxies from the original images. We detect a zone of diffuse emission south west of the cluster center (DS1), and a second faint object (ComDif), within DS1. Another diffuse source (DS2) may be detected, at lower confidence level, north east of the center. These sources of diffuse light contribute to 10-15% of the total visible light in the cluster. Whether they are independent entities or are part of the very elliptical external envelope of the central galaxy remains unclear. VLT VIMOS integral field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif but do not allow to compute a redshift. A hierarchical substructure detection method reveals the presence of several galaxy pairs and groups defining a similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The analysis of archive XMM-Newton and Chandra observations shows X-ray emission elongated in the same direction. The X-ray temperature map shows the presence of a cool core, a broad cool zone stretching from north to south and hotter regions towards the north east, south west and north west. This possibly suggests shock fronts along these directions produced by infalling material. These various data are consistent with a picture in which diffuse sources are concentrations of tidal debris and harassed matter expelled from infalling galaxies by tidal stripping and undergoing an accretion process onto the central cluster galaxy; as such, they are expected to be found along the main infall directions.Comment: Accepted for publication in Astronomy and Astrophysic

The ACS LCID project. VI. The SFH of the Tucana dSph and the relative ages of the isolated dSph galaxies

We present a detailed study of the star formation history (SFH) of the Tucana dwarf spheroidal galaxy. High quality, deep HST/ACS data, allowed us to obtain the deepest color-magnitude diagram to date, reaching the old main sequence turnoff (F814 ~ 29) with good photometric accuracy. Our analysis, based on three different SFH codes, shows that Tucana is an old and metal-poor stellar system, which experienced a strong initial burst of star formation at a very early epoch (~ 13 Gyr ago) which lasted a maximum of 1 Gyr (sigma value). We are not able to unambiguously answer the question of whether most star formation in Tucana occurred before or after the end of the reionization era, and we analyze alternative scenarios that may explain the transformation of Tucana from a gas-rich galaxy into a dSph. Current measurements of its radial velocity do not preclude that Tucana may have crossed the inner regions of the Local Group once, and so gas stripping by ram pressure and tides due to a close interaction cannot be ruled out. On the other hand, the high star formation rate measured at early times may have injected enough energy into the interstellar medium to blow out a significant fraction of the initial gas content. Gas that is heated but not blown out would also be more easily stripped via ram pressure. We compare the SFH inferred for Tucana with that of Cetus, the other isolated LG dSph galaxy in the LCID sample. We show that the formation time of the bulk of star formation in Cetus is clearly delayed with respect to that of Tucana. This reinforces the conclusion of Monelli et al. (2010) that Cetus formed the vast majority of its stars after the end of the reionization era implying, therefore, that small dwarf galaxies are not necessarily strongly affected by reionization, in agreement with many state-of-the-art cosmological models. [abridged]Comment: Accepted for publication on ApJ, 19 pages, 10 figures, 2 tables. A version with full resolution figures is available at http://www.iac.es/project/LCID/?p=publication

Prospects for a Dark Matter annihilation signal towards the Sagittarius dwarf galaxy with ground based Cherenkov telescopes

Dwarf galaxies are widely believed to be among the best targets for indirect dark matter searches using high-energy gamma rays; and indeed gamma-ray emission from these objects has long been a subject of detailed study for ground-based atmospheric Cherenkov telescopes. Here, we update current exclusion limits obtained on the closest dwarf, the Sagittarius dwarf galaxy, in light of recent realistic dark matter halo models. The constraints on the velocity-weighted annihilation cross section of the dark matter particle are of a few 10$^{-23}$ cm$^{3}$s$^{-1}$ in the TeV energy range for a 50 h exposure. The limits are extrapolated to the sensitivities of future Cherenkov Telescope Arrays. For 200 h of observation time, the sensitivity at 95% C.L. reaches 10$^{-25}$ cm$^{3}$s$^{-1}$. Possible astrophysical backgrounds from gamma-ray sources dissembled in Sagittarius dwarf are studied. It is shown that with long-enough observation times, gamma-ray background from millisecond pulsars in a globular cluster contained within Sagittarius dwarf may limit the sensitivity to dark matter annihilations.Comment: 12 pages, 5 figures, 2 tables, accepted for publication in Ap

The Star Formation & Chemical Evolution History of the Fornax Dwarf Spheroidal Galaxy

We present deep photometry in the B,V and I filters from CTIO/MOSAIC for about 270.000 stars in the Fornax dwarf Spheroidal galaxy, out to a radius of r_ell\sim0.8 degrees. By combining the accurately calibrated photometry with the spectroscopic metallicity distributions of individual Red Giant Branch stars we obtain the detailed star formation and chemical evolution history of Fornax. Fornax is dominated by intermediate age (1-10 Gyr) stellar populations, but also includes ancient (10-14 Gyr), and young (<1 Gyr) stars. We show that Fornax displays a radial age gradient, with younger, more metal-rich populations dominating the central region. This confirms results from previous works. Within an elliptical radius of 0.8 degrees, or 1.9 kpc from the centre, a total mass in stars of 4.3x10^7 Msun was formed, from the earliest times until 250 Myr ago. Using the detailed star formation history, age estimates are determined for individual stars on the upper RGB, for which spectroscopic abundances are available, giving an age-metallicity relation of the Fornax dSph from individual stars. This shows that the average metallicity of Fornax went up rapidly from [Fe/H]<-2.5 dex to [Fe/H]=-1.5 dex between 8-12 Gyr ago, after which a more gradual enrichment resulted in a narrow, well-defined sequence which reaches [Fe/H]\sim-0.8 dex, \sim3 Gyr ago. These ages also allow us to measure the build-up of chemical elements as a function of time, and thus determine detailed timescales for the evolution of individual chemical elements. A rapid decrease in [Mg/Fe] is seen for the stars with [Fe/H]>-1.5 dex, with a clear trend in age.Comment: 18 pages, 20 figure